Many intensive medical treatments currently available require patients to have repeated injections of drugs. In circumstances where intravenous access is proven to be limited, patients may be advised to have a central venous access device such as a port or portacath surgically implanted beneath the skin. Various types of ports or portacaths are available and are available under trade names such as Port-a-Cath, Microport, Bardport, PowerPort (power injectable), Passport, Infuse-a-Port, Medi-Port, and Lifesite (for hemodialysis patients). Ports of this type may form part of what is known as a totally implantable venous access system (TIVAS). Long-term intravenous lines, in particular those used with the TIVAS mentioned above can cause in significant damage to the veins.
In general, the port comprises a reservoir compartment or portal, made up of a solid casing provided with an upper septum comprising a self-sealing material such as a self-sealing silicone. It further comprises a plastic tube that extends from the reservoir and forms a catheter.
In use, the port is surgically inserted under the skin in one of a number of possible locations around the body including the upper chest or in the arm of a patient where it projects upwardly and appears as a small bubble in the skin. The catheter that extends from the reservoir is surgically inserted into a vein, such as the jugular vein, subclavian vein, or superior vena cava.
To administer treatment using this system, the port is located and the surrounding area is disinfected. Treatments may be administered by accessing the port through the overlying skin and the septum using a needle such as a Huber needle. Treatments delivered via this route will be transfused readily throughout the body as they will pass directly into the vein via the catheter.
Ports of this type may be used in a variety of treatments including for example total parenteral nutrition, delivery of infusions in chemotherapy, delivery of coagulation factors, the withdrawing of blood from patients requiring frequent blood tests, delivery of antibiotics such as are used in the treatment of long-term conditions such as cystic fibrosis, and the delivery of various medications.
However, ports are of limited life and will need to be replaced at intervals. Although they may last 5-6 years, failure in much shorter periods, for example of 2 years or less are not uncommon. When the device fails, a further surgical operation is required to remove the port and to replace it with a new one at a different site within the body. As there are limited sites available for insertion of a port or portacath, it is important for patients who are likely to have a long term need of the port, such as cystic fibrosis patients, to ensure that the life of a port is as long as possible.
One reason for premature failure of a portacath is believed to the result of incorrect needle insertion. Inspection of portacaths that have failed after removal can reveal problems. In particular, needle insertion marks visible in the septum may be grouped closer to one side of the septum, or needle hits may also be found on the side walls of the casing of the portacath. Indeed, cracks through the casing are also found. These are very likely to be a direct result of the needle being inserted off-centre.
The usual procedure for inserting needles into a port is a manual one. After disinfection of the area over and around the port, a medical practitioner such as a nurse or doctor will hold the port with two or three fingers of one hand whilst inserting the needle with the other hand. During this manoeuvre, it can be difficult to hold the port still whilst inserting the needle. This is due to the fact that the port is attached to the inside of the body, which in itself is dynamic and is therefore prone to movement. FIG. 12A below shows a three-dimensional model of a port underneath the skin. The port (iii) is fixed to the subcutaneous body tissue (iv) but this means that it can pivot in any direction relative to the skin (v). The skin is fixed and the needle (vi) can move up and down along the central axis of the raised dome of the skin. Under these circumstances, although a needle looks like it is central to the port, FIG. 12B, in which the skin layer is removed, shows that the needle is in fact off-centre.
If the needle is not inserted centrally in the septum, it may strike the casing leading to pitting or cracking of the portacath and leading to premature failure.
Devices for facilitating accurate positioning of the needle are described for example in Japanese patent application No. JP2010172653 and U.S. Pat. No. 5,620,419. These provide for locator devices arranged to fit over the port whilst a needle is inserted into it. However, such devices are not readily available. One reason why such devices have not been widely adopted may be associated with the ease of use.
Once the needle is in position in the port, it is necessary to remove the locator from the vicinity of the needle, to allow the infusion process to proceed. JP2010172653 does not generally address this problem, although one embodiment is constructed in a two-part form that includes a complex comb structure to join the two elements together. This embodiment is a complex arrangement, which would be difficult to manufacture economically. In addition, the elements of the comb-like structure extend across the opening through which the needle is inserted, and so these elements may interfere with the injection and removal operation, potentially damaging the port.
The device of U.S. Pat. No. 5,620,419 provides an upwardly projecting flange to allow the device to be slid off. However, this is a delicate operation as the needle and wide pad at the top of the needle (found on the modern huber needles) if present is required to pass through a narrow radial slit increasing the risk of disturbance to the needle. Furthermore, the upwardly projecting flange may interfere with the injection operation itself.